The present invention relates to a method for manufacturing a pressure-measuring device equipped with a resonating element.
More specifically, the invention relates to a method for manufacturing a pressure-measuring device for measuring absolute, relative or differential pressure.
The pressure-measuring device that can be manufactured using the method according to the invention is, for example, of the type described in Italian patent application No. MI96A002268, filed in the name of the same applicant as the present application, the disclosure of which is incorporated herein for reference.
It is known that pressure-measuring devices can be prepared by suitably machining wafers of semiconductor-based materials.
In particular the technologies currently known and referred to as "silicon micromachining" are widely used for manufacturing sensors using silicon as the base material.
It is known that such micromachining technologies are very similar to those used for the production of microelectronic circuits. With a single process, it is possible to machine a considerable number of devices that are identical to one another with significant advantages in terms of production costs.
Micromachining generally comprises technologies such as thin layer deposition (a few microns thick) of semiconductor materials and their derivatives or metal materials, extremely precise photolithographic techniques (resolutions of less than one micron), selective removal of semiconductor material through the action of suitable chemical agents, bonding techniques on separate layers.
It is known from the literature that "silicon micromachining" technologies can be divided into two main categories known as "bulk micromachining" technologies and "surface micromachining" technologies.
The former refers to the possibility of obtaining monocrystalline structures by machining both sides of a wafer of semiconductor material, whereas the latter refers to machining performed on one side of the wafer only. "Bulk micromachining" technologies have been developed from crystal machining and are therefore highly consolidated. "Surface micromachining" technologies, on the other hand, are highly innovative compared to the former and make it possible to manufacture smaller microstructures (one order of magnitude smaller). They also offer the considerable advantage of easier machining and greater potential for integrating the structures produced with microelectronic circuits made in the same chip of semiconductor material.
The manufacture of pressure-measuring devices generally involves a number of manufacturing difficulties as described hereinafter, especially when high performances are required.
In the first place, the high number of manufacturing process phases makes the manufacture of the pressure sensor costly. Moreover, the devices of known type are often based on polysilicon and quartz and their mechanical performances are not optimal. Also, in most cases, both sides of the wafer are subjected to very critical machining steps, thus complicating the manufacturing process.